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The Impact of Comprehensive Chromosomal Screening on IVF Embryo Selection

A recent study looked at embryo selection in an IVF cycle based on two different criteria: embryo morphology and chromosomal makeup. Researchers looked at day 5 embryos (blastocysts) that were graded using standard morphology, then tested with comprehensive chromosomal screening (CCS). The study concluded that when embryos are selected to transfer based solely on morphology, in 41% of cases the embryos chosen will be aneuploid (abnormal).

Morphology uses a grading system to rate embryos based on the appearance of the embryo and certain characteristics, including the number of cells and how fast it is growing. With CCS, the embryos are biopsied to determine their genetic makeup.

The study, which included researchers from Colorado Center for Reproductive Medicine, analyzed 2,670 blastocyst CCS cycles from 2010-2014. The highest grade embryos were discovered to be aneuploid in 41% of the IVF cycles. Older women had a larger number of high grade blastocysts that were aneuploid. “The transfer of an aneuploidy embryo will always result in failed implantation, miscarriage or an affected fetus,” the study says.

“The embryos’ grade and how they look, and their chromosomes don’t really correlate well,” says Dr. William Schoolcraft, Founder and Medical Director of Colorado Center for Reproductive Medicine. “If we came to find that when embryos are graded “AA”, 90% are genetically normal and when they’re “CC”, 90% are genetically abnormal, at some point you could probably say we don’t have to keep screening the embyros – you can correlate their grade with their probability of aneuploidy and that’s good enough. But it’s just the opposite. There’s almost no correlation between the quality and the grade.”

The 41% aneuploidy rate is in line with past success IVF success rates, when pregnancy rates were lower and miscarriage rates were higher. CCS helps identify a normal embryo for transfer, and reduces the miscarriage rate, particularly in older women. The miscarriage rate for a 40-year-old might be as high as 40%, but with CCS tested embryos it’s 6%, Schoolcraft says. “I think it says clearly that the majority of miscarriages are due to chromosomal errors because when you screen for that one variable you eliminate 94% of them.”

Patients need to keep in mind that success with CCS is contingent on getting a chromosomally normal embryo. It doesn’t help you produce more normal embryos, rather it helps determine which embryos you produce are normal, if any.